Having been strikingly developed, recent semiconductor technology involves principally the integration of more than a million cells, the establishment of a great number of input/output (I/O) pins on non-memory devices, large die sizes, the radiation of extensive heat, high electrical performance, etc. In spite of its remarkable advance, the semiconductor technology is not completely practiced because electronic package technology has not yet developed to such a level as to back the semiconductor technology. In pursuit of high electric performance, microminiaturization/high density, low-power operation, multifunction, high-speed signal processing, permanent reliability, etc., the electronic package technology is one of the most important factors which have critical influence on the determination of a final product's values, including performance, size, price, reliability, etc. Indispensable applications of microminiaturized package assemblies exist in the recently rapidly growing electronic industries, for example, in the computer, information communication, mobile communication, and high-tech electronic appliance industries. In particular, flip chip technology finds numerous applications in the smart card, liquid crystal display (LCD), plasma display panel (PDP), computer, cellular phone, and communication system industries.
Such flip chip technology has been and is being developed from a connection process using solders to a connection process using conductive adhesives which have advantages of the ability to pitch microelectrodes at low costs, fluxless, environment-friendly processing, and low temperature processing.
Commercially available as an anisotropic conductive film/adhesive type and an isotropic conductive adhesive type, conductive adhesives are composed normally of conductive particles, such as Ni, Au/polymer, and Ag, and thermosetting or thermoplastic insulating resins. Undoubtably, a conductive adhesive which is of more reliability, lower resistance and higher adhesive strength guarantees a better flip interconnection on an organic substrate. For this, necessary is knowledge of the optimal values for the size, distribution, content, and strain modulus of the conductive particles. In addition, it is also required to develop an adhesive resin capable of being cured within a shorter time at a lower temperature, its preparation process, and an ACA which can afford a flip chip process of low cost.
Typically, ACAs are divided into a film type and a paste type. The invention is primarily to develop a paste type of ACAs, which are useful for the interconnection of flip chips on plastic substrates, with the aim of making simple the manufacture of them.
Because flip chip technology using conductive adhesives has not yet been standardized clearly, Hitachi and Sony, leading companies in the conductive adhesive field of the world, European universities which form a multinational research consortium in which conductive adhesives are under systematic study, and company research institutes of many countries keenly compete with each other to dominate the world market through the world standardization of their own products. In particular, electronic package technology, one of the most important fields in producing electronic products, attaches great importance to the materials to be used and their preparation processes. Under this condition, novel connection materials which can replace conventional solder material to meet the tendency toward environment-friendly products as well as guarantee electrical conductivity and reliability are needed and their development is being watched with keen interest.
Prior arts which are relevant to the invention include (1) no-flow underfill technology and (2) conventional ACA. Quite different from the invention, the former, in which an underfill is formed when a solder-formed substrate is connected onto a substrate, does not use conductive particles. The latter suffers from a problem in that it is not of high reliability owing to high thermal coefficient resulting from the existence of oily conductive particles in ACA.